Ferromagnetic glasses based on ferrous metals (i.e. metals from the Iron Triad) Fe, Co, and Ni and bearing metalloids such as P, C, B, and Si have been known since the early 1970's. These early glasses exhibited soft ferromagnetic properties, and were only capable of forming glasses that were a few micrometers thick. Fe—Si—B and Fe—P—C are two example systems of such ferromagnetic glass formers. More recently, it was discovered that incorporating small fractions of non-ferrous transition metals in these early compositions leads to ferromagnetic glasses that can be formed in bulk dimensions, that is, formed into sections that are at least 1 mm thick. Examples include Fe—Ni—P—C—B with an addition of about 5 atomic percent Mo, and Fe—Co Si—B or Fe—Ni—Si—B with an addition of about 5% Nb. All of these cases led to ferromagnetic bulk-glass formers capable of forming glassy rods greater than 1 mm in diameter.
In these systems, while small additions of non-ferrous transition metals such as Mo and Nb have been shown to dramatically enhance the glass-forming ability of these early marginal glass formers, they also degrade the ferromagnetic performance of these alloys, as they lead to lower saturation magnetization and higher coercivity and remanence. It would therefore be of interest to discover ferromagnetic bulk-glass formers that are free of non-ferrous transition metals such that they combine the superb ferromagnetic performance of the early glassy ferromagnets with the capability to form bulk glassy components.
Recently, Li et al. (X. Li, Y. Zhang, H. Kato, A. Makino, and A. Inoue, “The Effect of Co Addition on Glassy Forming Ability and Soft Magnetic Properties of Fe—Si—B—P Metallic Glass”, Key Engineering Materials 508, 112-116 (2012), the reference of which is incorporated herein in its entirety) have investigated the Fe—Co—Si—B—P system. They replaced Fe with Co in a unique metalloid moiety with the atomic concentrations of Si, B, and P fixed at 9, 10, and 5 percent, respectively. By means of an ultra-high quench rate processing method (copper mold casting), they determined the largest critical rod diameter associated with that metalloid moiety to be 3 mm.